The present invention relates in general to methods and apparata for inductively heating and quench hardening a crankshaft. The broad scope of the present invention relates to inductively heating and quench hardening a crankshaft, which may be oriented either horizontally or vertically, wherein the induction coil assembly (or assemblies) do not contact the surfaces of the crankshaft which are to be induction hardened. Computer controlled servomotors and X and Y drive systems are used to position and move the induction coil assembly relative to a crankpin portion of the crankshaft as the crankshaft rotates at a predetermined RPM. The travel of the induction coil assembly is based upon mathematical formulae and the crankshaft geometry, including crankshaft dimensions and the particular location of the crankpin portion to be induction hardened relative to the longitudinal axis of the crankshaft. More specifically, the present invention focuses on the design of an induction coil for a crankshaft having a split-pin construction.
An automotive crankshaft is made up of a series of crankpins, one for each cylinder, in the case of in-line engines, or one for each pair of cylinders, in the case of V-type engines. The function of the crankshaft is to convert the reciprocating motion of the piston and its connecting rod into rotating motion. The throw of the crankshaft is equal to the stroke of the engine. The crankshaft needs to be properly balanced in order to eliminate centrifugal forces and accordingly the crankshaft is counterbalanced by weights placed opposite to the corresponding crankpins or just xe2x80x9cpinsxe2x80x9d. Each pin is received within one end of a corresponding connecting rod whose opposite end is pinned to a piston. Crankshafts are also configured with axial bearing surfaces which are designed for receipt by the main bearings. A six cylinder in-line crankshaft would typically have seven main bearings.
Due to the load and wear on the pins and on the bearing surfaces, the hardening of these portions of the crankshaft is important. One approach to this task is to inductively heat and then quench harden these critical surfaces. Traditionally the approach which has been followed is to place the crankshaft in a horizontal orientation and as the crankshaft reaches a substantially elevated temperature due to the induction heating, a support member is moved into position in order to support the crankshaft and keep it from sagging. This traditional approach also involves the induction coil and/or some portion of the induction coil assembly contacting and in fact actually riding on the surfaces which are to be inductively heated and quench hardened. This metal-to-metal contact accelerates the wear on the coil assembly, necessitating that the coil assembly be replaced periodically. The need to replace the induction coil assembly represents not only an added cost factor but also down time to the induction hardening equipment.
By orienting the crankshaft horizontally, the contact by the induction coil assembly on the critical surfaces of the crankshaft is actually encouraged due to the convenience of letting the induction coil assembly xe2x80x9cridexe2x80x9d on the pins and bearing surfaces as the crankshaft is rotated between centers. This traditional approach of having the induction coil assembly function like a follower does not require any separate drive system for the induction coil assembly since the critical surfaces are in contact with the coil assembly. However, direct contact between the coil assembly and the portion of the crankshaft to be induction hardened is seen as a substantial disadvantage, not only due to wear of the induction coil assembly and the horizontal mounting of the crankshaft, but for the additional reasons which are set forth below.
When the induction coil assembly contacts the pins and/or bearing surfaces, it is difficult to identify the wear condition of the coil assembly. By riding directly on the crankshaft surfaces, the contacting surface of the induction coil assembly is effectively hidden from view, thereby making it difficult to assess the level or degree of wear on the coil assembly. This in turn means that the induction coil assembly can be run too long and reach a point at which it arcs out and this typically ruins the part and ruins or damages the coil assembly. Contact between the coil assembly and the crankshaft often results in marring or galling of the crankshaft surface and this requires extra grind stock which can then be machined away in order to grind out the surface imperfections. An extended post-hardening step is then required. It would be a substantial improvement to the present methods and apparata for induction hardening crankshafts if an apparatus could be provided whereby the induction coil assembly does not have to contact the pins and bearing surfaces. Such an apparatus would significantly improve coil assembly life.
According to the present invention, one induction coil assembly is provided for the crankshaft pins and may be located and operated at a first workstation. Either a separate induction coil assembly or a series of coil assemblies are provided for the bearing surfaces and may be located and operated at a second workstation. These coil assemblies are designed such that there is no contact with the crankshaft surfaces which the coil assemblies are to induction harden. This improves the coil assembly life. According to the present invention, the dimensions and geometry of the crankshaft are used to define the path or orbit of each pin and the tracking path for each induction coil assembly is computed and programmed into suitable drive systems which control the travel of each coil assembly. While the bearing surfaces also have an orbit, these orbits are concentric with the axis of rotation of the crankshaft. Accordingly the coil assembly (or assemblies) used for these bearing surfaces does not have to travel in a matching orbit, but instead is stationary.
While induction hardening of crankshafts is known, the present invention remains novel and unobvious. The combination of structural features of the present invention, including the induction coil designs which are disclosed, provide significant advantages to what presently exists and the long felt and heretofore unsatisfied need for the present invention validates its novel and unobvious advance in the art.
An induction hardening coil assembly for induction hardening of a workpiece according to one embodiment of the present invention comprises a coil having a top surface, an underside surface, and an inner coil curvature disposed between the top surface and the underside surface, the inner coil curvature extending approximately 180 degrees around a coil axis, the coil further including a first end section adjacent a first end of the inner coil curvature and extending between the top surface and the underside surface and a second end section adjacent a second end of the inner coil curvature and extending between the top surface and the underside surface, and a support arm connected to the coil and being constructed and arranged for providing an electrical connection between the coil and a source of electrical current, the support arm including a current-in portion connected to the top surface via said first end section and a current-out portion connected to the underside surface at a location which is between the first and second side surfaces.
One object of the present invention is to provide an improved induction hardening coil for the induction hardening of a workpiece.
Related objects and advantages of the present invention will be apparent from the following description.